1. Field of Invention
The present invention relates to aligning a thin-film transistor (TFT) plate with a color filter plate of a thin-film transistor liquid-crystal display (TFT LCD). More particularly, the present invention relates to shifting the color filter plate relative to the TFT plate, and then aligning them, to overcome the phenomenon of corner image sticking.
2. Description of Related Art
In the manufacturing process of a TFT LCD, a TFT plate and a color filter plate are manufactured first, the LCD is then formed, and finally the LCD module is formed. A TFT plate is also called an array plate.
In the stage of LCD formation, a rubbing process is performed on the TFT plate and the color filter plate, and then the TFT plate and the color filter plate are aligned. FIG. 1 is a partial cross-sectional view of the alignment of a TFT plate and the color filter plate. With reference to FIG. 1, the color filter plate has a substrate 102, a black matrix 104 formed on the substrate 102, and a color filter layer comprising a red (R) color resist 106 and a green (G) color resist 108. The red color resist 106 and the green color resist 108 are also formed on the substrate 102, and they partially overlap and cover the black matrix 104 in order to avoid light leakage. The color filter plate also has an electrically conductive layer (not shown in FIG. 1) acting as an electrode, which is formed to cover the red color resist 106, the green color resist 108, and the black matrix 104.
Still referring to FIG. 1, the TFT plate has a substrate 110 and a pixel electrode layer 112 formed on the substrate 110. The pixel electrode layer 112 has capacity storage areas 114 and 116, which are designed within a black matrix area of the color filter plate, that is, within the black matrix 104. Bumps 118 and 120 usually exist in the capacity storage areas 114 and 116. As shown in FIG. 1, the rubbing direction associated with the TFT plate and the color filter plate is from left to right. Prior to the rubbing process, a resin coating is formed on the TFT plate and on the color filter plate. The resin usually comprises polyimide, which is abbreviated as PI in the LCD industry. The rubbing process is performed by using a metal roller, covered with a nap cloth, to rub the resin coating, or rotating the roller to and fro along the surface of the resin coating, with the purpose of making subsequently placed liquid crystal molecules face in a specified direction in advance.
In FIG. 1, the overlapping portions of the color filter layer and the black matrix 104 cause height differences, and the bumps 118 and 120 on the TFT plate also cause height differences. When the rubbing direction is from left to right, the height difference x associated with the color resist 108 and the height difference y associated with the bump 120 result in regions where the resin coating there cannot be rubbed well, resulting in, for example, the abnormal rubbing areas 124 and 122, respectively. In addition, when the TFT plate and the color filter plate are aligned, the abnormal rubbing areas 124 and 122 overlap and are aligned. When the rubbing direction is from right to left, abnormal rubbing areas occur on the red color resist 106 and on the pixel electrode layer 112 adjacent to the bump 118, respectively.
The above-mentioned abnormal rubbing areas can cause the problem of corner image sticking in a frame displayed on the liquid crystal display. Since abnormal rubbing areas in the black matrix area are blocked by the black matrix 104, light leakage doesn't occur; on the other hand, since the abnormal rubbing areas 124 and 122 are within the display area, light leakage occurs and results in corner image sticking. The phenomenon of corner image sticking is illustrated in FIG. 2. When the lamps of the LCD panel are illuminated, there are white strip areas 202 and 204 on the four side edges of the corner image sticking examination frame 200. After the corner image sticking examination frame 200 switches to the fully black frame 206, some spots in the white strip areas 202 and 204 cannot turn dark, resulting in the phenomenon of corner image sticking 208. This is due to the larger thickness of the PI resin coating at the four side edges of the panel; the degree to which the resin coating on the abnormal rubbing areas cannot be rubbed is thus more serious, more easily causing the corner image sticking.